Molybdenum-based precipitates are useful as raw materials for molybdenum-based solid catalysts used, for example, in the production of methyl tert-butyl ether by the etherification of isobutene and methanol, the production of methacrylic acid by the dehydrogenation of isobutyric acid, and the production of methacrylic acid by the vapor phase catalytic oxidation of methacrolein, and active investigations are being carried on for purposes of industrial production. In the prior art, a large number of propositions have been made as to the compositions of such catalysts and the preparation processes thereof. Generally, it is known that a molybdenum-based precipitate can be formed by allowing an oxoacid ion containing the element A to exist in an aqueous solution of a molybdate and acidifying the solution.
However, Conventional processes for the preparation of a molybdenum-based precipitate may fail to yield a molybdenum-based precipitate having a sufficiently high purity and a desired average particle diameter.
Moreover, most of the conventional processes for the preparation of a molybdenum-based precipitate are concerned with the preparation of a molybdenum-based precipitate containing one or two metallic elements. Few reports have been made of a process which can also be suitably applied to the preparation of a molybdenum-based precipitate containing three or more metallic elements.
On the other hand, a number of propositions have conventionally been made as to the method of washing a molybdenum-based precipitate. However, conventional methods for washing a molybdenum-based precipitate are disadvantageous in that impurities cannot be fully removed or a considerable change in average particle diameter may occurs during washing.
In particular, the average particle diameter of a molybdenum-based solid catalyst is an important factor which determines the pore distribution and other properties of the solid catalyst and hence contributes greatly to its performance such as catalytic activity and selectivity. Nevertheless, there have been few reports which disclose a method for washing a molybdenum-based precipitate efficiently while suppressing a change in the average particle diameter thereof.
Moreover, most of the conventional method for washing a molybdenum-based precipitate are concerned with the washing of a molybdenum-based precipitate containing one or two metallic elements. Few reports have been made of a method which can also be suitably applied to the washing of a molybdenum-based precipitate containing three or more metallic elements.
In view of the above-described circumstances, an object of the present invention is to provide a process which permits a molybdenum-based precipitate having a high purity and a desired average particle diameter to be conveniently prepared with good workability, and which can be suitably applied to the washing of a molybdenum-based precipitate containing three or more metallic elements.
Another object of the present invention is to suppress a change in the average particle diameter of a molybdenum-based precipitate, wash it conveniently with good workability, and thereby obtain a molybdenum-based precipitate having a high purity and a desired average particle diameter. A further object of the present invention is to wash a molybdenum-based precipitate containing three or more metallic elements in a suitable manner.